JPH0251891A - Thin film el element - Google Patents

Abstract

PURPOSE:To make a corresponding time of CaS:Eu red EL element to be reduced by adding an element which emits light strongly absorbed to Eu and CaS:Eu such as Ce, Pr, Tm, etc., to a CaS:Eu emission layer. CONSTITUTION:An element where an emission layer 4 consisting of a matrix material CaS and a luminescence center Eu is sandwiched in insulting layers 3 and 5 which is a red emitting EL element emitting with application of AC voltage to the emission layer 4 through an electrode 6 installed on the surface of the insulating layer 5 and makes EL emission in Eu and CaS such as Ca, Pr, Tm, etc., whose emitting light energy is within the range of approx. 2.3-2.6eV wherein CaS:Eu is strongly absorbed is added. Thereby, the corresponding time of CaS:Eu element is shortened to 10ms-100ms.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a material structure of a light emitting layer of a thin film EL device.

[Conventional technology]

Regarding the slow luminance response of conventional CaS:Eu red EL elements, see Applied Physics Letters, 50.
(1987) pages 641 to 643 (A
pplied Physics Letters
, p. 641-643 (1987)).

[Problem to be solved by the invention]

The above-mentioned conventional technology does not take into account the time required for the luminance to reach the saturation value after the start of driving (hereinafter referred to as response time). In general, an EL element emits light by direct collision excitation of a luminescent center while conduction electrons reciprocate in a luminescent layer sandwiched between insulating layers by an AC driving IJjJ voltage. In order to excite the luminescent center Eu of the CaS:EuEL element with this luminescent mechanism, the practical driving frequency is 60
When driven with a Hz AC symmetrical pulse waveform, the response time takes several seconds to several tens of seconds. This poses a problem in that CaS:Eu cannot be used as a red light-emitting material for a full-color EL display for displaying moving images, which requires real-time response to driving.

The purpose of the present invention is to reduce the response time of CaS:Eu red EL devices.

[Means to solve the problem]

The above purpose is to add Ce and Pr in addition to Eu to the CaS:Eu light emitting layer.
, Tm, etc., which emit light that is strongly absorbed by CaS:Eu.

[Effect]

CaS: When Eu is directly excited by conduction electrons flowing in the light-emitting layer in an EuEL device, the energy of the conduction electrons is about 4 eV, and the energy required to excite Eu is about 1.9 eV, so the energy of the conduction electrons is about 2. 1 eV
Eu is excited after dissipating the energy in the light emitting layer. In CaS:Eu, there are few processes to dissipate energy of about 2.1 eV, so it takes time for conduction electrons to excite Eu, and it is thought that the brightness response time becomes longer.

On the other hand, the energy required to excite Eu co-activators such as Pr, Ce, and Tm is 2.3 eV to 2.6
eV, and the energy that a conduction electron with an energy of about 4 eV must dissipate to excite these coactivators is 1
, 4 to 1.7 eV, which is lower than the energy that must be dissipated to directly excite Eu.
The time required to excite Tm, etc. is generally considered to be short, and experimentally, CaS:Pr, Ca, S:Ce, Ca
The response time of the S:TmEL element at a driving frequency of 60 Hz is as short as about 10 m5.

On the other hand, CaS:EuEL devices have an energy range of 2.3 to 2
, 6eV (wavelength range 440-480nm), which corresponds to the energy of light emitted by Pr+Ce, Tm, etc. Therefore, by adding Pr, Ce, Tm, etc. as co-activators to the CaS:Eu light emitting layer of the CaS:EuEL device, the response time of the CaS:EuEL device can be reduced from the conventional several seconds to tens of seconds to 10 ms. ~1
The reason why the light emission is shortened to 00 m s is that the conduction electrons do not directly excite Eu to emit light, but the conduction electrons excite the co-activators Pr, Ce, Tm, etc., and the light emitted by them. This is thought to be because light emission occurs when Eu is excited.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing a cross-sectional view of a CaS:EuEL device according to an embodiment of the present invention. A transparent electrode 2 made of ITO is deposited on a glass substrate 1 (for example, Corning #7059). A transparent lower insulating layer 3 made of Tazo 5 or the like is deposited thereon to a thickness of about 0.5 μm by high frequency sputtering or the like. Furthermore, on top of that
Eu as 0.3 mo1%, Ce as co-activator Q
, l A light emitting ff4 made of CaS containing 1% of mole is deposited to a thickness of about 1.0 μm by electron beam evaporation or the like. The co-activator is other than Ce.

Any element, such as Pr or Tm, may be used as long as it emits EL light in CaS and the energy of its emission spectrum is within the range of about 2.3 to 2.6 eV. Furthermore, for example, Ta
An upper insulating layer 5 made of zOb or the like is deposited to a thickness of about 0.5 μm by high frequency sputtering or the like. Finally, a back electrode made of Aff or the like is deposited thereon.

FIG. 2 is a diagram showing the voltage dependence of the luminance response time at a driving frequency of 60 Hz of a Ca,S:EuEL element according to an embodiment of the present invention. The voltage on the horizontal axis is shown as an increase in voltage from the emission start voltage. As shown in the figure, the response time of a conventional EL device containing only 0.3 mo1% of Eu in the CaS light emitting layer is several S to several tens of S, whereas Ce is 0.01. m
As a result of adding o1%, the response time is 10m5 to 100m
It was possible to reduce it to s.

〔Effect of the invention〕

According to the present invention, the luminance response time of the CaS:EuEL element, which has been a problem in the past, can be reduced to several S at a driving frequency of 60 Hz.
It has the effect of shortening the length from several tens of S to 10m5 to 100m5, which is required as a red light emitting material for a full color EL display for displaying moving images.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing one embodiment of the present invention, and FIG. 2 is a diagram showing the effect on the luminance response time of the element according to one embodiment of the present invention. 1... Glass substrate, 2... Transparent electrode, 3... Lower insulating layer.・Light-emitting layer. 5... Upper insulating layer, - Back electrode. Figure Figure

Claims (1)

[Claims] 1. A red light-emitting E that emits light by sandwiching a light-emitting layer consisting of a matrix material CaS and a luminescent center Eu between insulating layers and applying an alternating current voltage to the light-emitting layer through an electrode provided on the surface of the insulating layer.
In the L element, in addition to the emission center Eu, there is C in the CaS matrix.
e, Pr, Tm, etc. emit EL in CaS, and the energy of the emitted light is strongly absorbed by CaS:Eu, about 2.3
A thin film EL device characterized in that an element within the range of ~2.6 eV is added.